Combination current sensor and relay

ABSTRACT

A protection device for monitoring current in a power cable to an electrical device and for controlling a remotely located starter for the electrical device in response to a system controller. The device includes a transformer magnetically linked with the power cable to produce a voltage signal in response to the presence of a changing current within the power cable. An input circuit located in a single housing together with the transformer is electrically connected to the transformer so as to receive the voltage signal. The input circuit produces, in response to the voltage signal, either a first signal or a first circuit condition at the output terminal of the input circuit, representative of the changing current in the power cable. A switch circuit also in the same container with the transformer has a terminal for sensing either a second signal or a second circuit condition of the remotely located system controller. The switch circuit has a second terminal to provide either a third signal or a third circuit condition effective to control the starter, in response to sensing one of the second signal and the second circuit condition. All of the transformer, the input circuit, and the switch circuit are located in a single unitary package which is easily mounted and adjusted to a desired position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/383,231. Filed Mar. 20, 2009, which is a continuation of U.S. patentapplication Ser. No. 12/070,606, filed Feb. 19, 2008, now U.S. Pat. No.7,548,404, which is a continuation of U.S. patent application Ser. No.11/732,659, filed Apr. 3, 2007, now U.S. Pat. No. 7,362,556; which is acontinuation of U.S. patent application Ser. No. 11/187,053, filed Jul.21, 2005, now U.S. Pat. No. 7,203,047; which is a continuation of U.S.patent application Ser. No. 10/902,395, filed Jul. 28, 2004, now U.S.Pat. No. 6,950,292; which is a continuation of U.S. patent applicationSer. No. 10/772,187, filed Feb. 3, 2004, now U.S. Pat. No. 6,888,712;which is a continuation of U.S. patent application Ser. No. 10/052,248,filed Jan. 18, 2002, now U.S. Pat. No. 6,724,600; which is acontinuation of U.S. patent application Ser. No. 09/748,084, filed Dec.20, 2000, now U.S. Pat. No. 6,377,430; which is a continuation of U.S.patent application Ser. No. 09/438,216, filed Nov. 12, 1999, now U.S.Pat. No. 6,219,216; which is a continuation of U.S. patent applicationSer. No. 09/264,367, filed Mar. 8, 1999, now abandoned; which is acontinuation of U.S. patent application Ser. No. 09/057,730, filed Apr.8, 1998, now U.S. Pat. No. 6,005,760; which is a continuation of U.S.patent application Ser. No. 08/500,522, filed Jul. 11, 1995, now U.S.Pat. No. 5,808,846.

BACKGROUND OF THE INVENTION

The present invention relates to a single protection device, including atransformer, an input circuit, and a switch circuit, suitable foraddition to an electrical power system that includes a control panelelectrically interconnected with a starter to control an electricaldevice. It is desirable to monitor the performance of devices such aselectric motors and to control them through remotely located controlpanels. While this has long been possible, it has been costly to installthe required sensors and controls.

Springer, U.S. Pat. No. 4,885,655 discloses an integratedcapacitor-start, induction-run electric motor starter and protectioncircuit specifically suitable for a water pump. The circuit requiresphysical electrical connection to the power cables to sense the phaseangle between the voltage and the current applied to the motor toindicate when it is operating without a load. When such a conditionoccurs, the circuit triggers an activator coil to de-energize the motorby opening a switch member. The integrated starter and protectioncircuit is suitable only for induction machines.

Libert, U.S. Pat. No. 4,887,018, discloses a start-up circuit forgradually starting a multiphase motor and which also includes detectorcircuits for detecting various fault conditions and for disconnectingpower from the motor in response to fault conditions. Integrating themotor starter and protection circuit into one device makes it unsuitablefor addition to existing power systems to detect fault conditions withinpower cables.

Flückiger, U.S. Pat. No. 5,359,273, discloses a load control circuit forcontrolling the load of an asynchronous motor. The circuit includes apair of capacitors, one of which can be connected in parallel with theother by a switch. Control over whether one or two capacitors issupplied as a load to the motor is provided by comparing signals from acurrent sensor and a voltage sensor in a comparator. Depending upon therelative size of the compared signals, the switch is turned off or on.

Domshy, et al., U.S. Pat. No. 3,593,078, discloses a starting andoperating control circuit that includes voltage sensors and currentsensors to start a motor and limit the power supplied to it.

One design of a starter includes an integrated starter and protectioncircuit to detect fault conditions of an associated electrical deviceand, in response to detecting a fault condition, disable the electricaldevice. When a starter with an integrated starter and protection circuitis used to control devices in an environment in which the electricaldevices are not dependent upon other machines, or their operation doesnot impact other devices, the inclusion of the integrated starter andprotection circuit is an effective way to protect the associatedelectrical device. However, when a starter including such an integratedprotection circuit is used in a system where the associated electricaldevice is interdependent with other electrical devices, use of such astarter to independently enable and disable the electrical device mayresult in devastating effects to the entire system. In other words,where several electrical devices combine to produce a result, as insystems that include a computerized control panel or system controller,it is desirable for the control panel or system controller to maintaincontrol over the status of the electrical devices to minimize potentialproblems.

However, many starter designs do not include an integrated protectioncircuit and also include no-fault detection. To provide fault detectionfor electrical devices, a current sensor surrounding the power cable tothe electrical device may be used to sense the electrical load current.The current sensor may be electrically interconnected between a controlpanel and the power cable to provide a signal to the control panelrepresentative of the current within the power cable. Suitable currentsensors are known, such as the current sensor sold by Veris Industries,Inc., under the trademark HAWKEYE 700. It is desirable to locate such acurrent sensor within a housing where a starter for the electricaldevice is located.

A relay is typically electrically interconnected between a remotelylocated control panel and a starter to receive a control signal from thecontrol panel and in response to provide an indication to the starter.Like the current sensor, such a relay may be located within a starterhousing.

The relay and current sensor in the past have been separate individualdevices, each requiring a mounting location that may not be availablewithin the starter housing due to limited space. Additionally, it takesadditional time to install two separate devices and requires stockingtwo separate replacement parts for use in the event of device failure.Also, trouble-shooting likely requires the inspection of both devices.

What is desired, therefore, is a protection device that is suitable foraddition to existing electrical systems that operate in an environmentincluding a control panel and a starter controlling the operation of anassociated electrical device. The protection device should be compact,inexpensive, and fast to install.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes the aforementioned drawbacks andshortcomings of the prior art by providing a protection device formonitoring current in a power cable to an electrical device and forcontrolling a starter for the electrical device in response to aremotely located system controller. The protection device includes atransformer magnetically linked with the power cable connected to theelectrical device. The transformer produces a voltage signal in responseto the presence of a changing current within the power cable. An inputcircuit located proximate to the transformer has an output terminal andis electrically connected to the transformer so as to receive thevoltage signal. The input circuit produces, in response to receiving thevoltage signal, one of a first signal representative of the changingcurrent and a first circuit condition at the output terminal of theinput circuit representative of the changing current in the power cable.A switch circuit has a first terminal for sensing one of a second signaland a second circuit condition of the remotely located systemcontroller. The switch circuit has a second terminal to provide one of athird signal or a third circuit condition, in response to sensing one ofthe second signal and the second circuit condition. The third signal andthe third circuit condition is effective to control the starter when thestarter is electrically connected thereto. All of the transformer, theinput circuit, and the switch circuit are located in a single unitarypackage.

By locating the sensor circuit, which is a combination of thetransformer and the input circuit, and the switch circuit proximate toone another within the single package, significant advantages arerealized. Due to the limited available space within a starter housing,the single package is more desirable. The expense of manufacturing asingle package is frequently less than manufacturing two separatepackages. The time required to install both the switch circuit and thesensor circuit is reduced by only requiring installation of one combinedpackage. A reduction in the number of backup parts and troubleshootingtime is also realized.

In a preferred package a mounting bracket includes a slide arrangementto support the transformer so that its position can be adjusted easilyto the best location with respect to the power cable.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic representation of an electrical system thatincludes a protection device according to the present invention, acontrol panel, and a starter controlling the operation of an associatedelectrical device.

FIG. 2 is a pictorial representation of the protection device of FIG. 1,showing a transformer, an input circuit, and a switch circuit.

FIG. 3 is an electrical schematic diagram of a transformer and inputcircuit which is a portion of a first embodiment of the presentinvention, suitable to provide a full scale 0 volt to 5 volt outputsignal.

FIG. 4 is an electrical schematic diagram, of a transformer and inputcircuit which is a portion of a second embodiment of the presentinvention suitable to provide an open circuit or short circuitcondition.

FIG. 5 is an electrical schematic diagram of a transformer and inputcircuit which is a portion of third embodiment of the present invention,suitable to provide a 4-20 ma output signal.

FIG. 6 is an electrical schematic diagram of a switch circuit includinga relay, which is a portion of one embodiment of the present invention.

FIG. 7 is an electrical schematic diagram of a switch circuit includinga triac, which is a portion of another embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIG. 1, an electrical system 10 includes a control panel 20that utilizes a digital computer to provide effective control of manyassociated electrical devices. The centralized control panel 20determines the effects on the entire system 10, or a portion of thesystem 10, of enabling or disabling an electrical device. For example,such associated electrical devices may include motors, pumps, fans,valves, generators, switches, lights, etc. One type of control panel 20is generally known as a programmable logic controller, such as thosesold by Allen Bradley.

A starter 22, designed to start (energize) and stop (de-energize)remotely located electrical devices, is electrically connected to anassociated electrical device 24 by three power cables 23 a, 23 b, and 23c. Each starter 22 is usually located within an individual starterhousing 26 which is a part of a substation. Most substations are notlarge, so it is desirable to reduce the size of the housing 26, so as tomaximize the number of housings 26 that may be located within thesubstation. Accordingly, the housing 26 is normally designed to be onlyslightly larger than the enclosed starter 22, and so there is onlylimited space within the housing 26 in which to place additionaldevices, such as protection devices.

Referring to FIG. 2, a protection device 35 includes both a currentsensor, including a transformer 34 and an input circuit 50, and a switchcircuit 60 within the single package 30. The package 30 is preferablyslidably mounted on a support 31 mounted within the housing 26. Byplacing the transformer 34, input circuit 50, and switch circuit 60proximate to one another, within the single package 30, it isconsiderably easier to locate the device 35 within the limited space ofthe starter housing 26. Additionally, installing only the single package30 requires less installation time than installation of separate devicesto perform each of the desired functions, and the expense ofmanufacturing, packaging and shipping a single device is less than fortwo separate devices. A reduction in the number of backup parts andtroubleshooting time is also realized.

The package 30 defines a central opening 32 through which the powercable 23 c is routed. Surrounding the central opening 32 is a toroidalsensing transformer 34 to sense the changing current within the powercable 23 c. The toroidal sensing transformer 34 is preferably awire-wrapped magnetically permeable toroidal core, normally made ofiron, encircling the respective power cable. Thus, the wire wound on thetoroidal sensing transformer 34 is the secondary winding, while thepower cable 23 c, or a parallel shunt current divider (not shown), isthe primary winding of the toroidal sensing transformer 34. Changingcurrent in the power cable 23 c induces a changing electromagnetic fieldaround the power cable 23 c, which in turn induces a magnetic flux inthe magnetically permeable core. The magnetic flux in the core inducesin the wire windings on the toroidal core a voltage representative ofthe current in the power cable. An exemplary sensing transformer has thefollowing construction: core material made by Arnold Engineering, ofNorfolk, Nebr., of 0.012 silectron, 3% silicon steel, grain oriented,with an outside diameter of 1.375 inches, an inside diameter of 1.125inches, strip width of 0.500 inches, strip thickness of 0.012 inches, anepoxy powder coating of 0.010 to 0.030 inches thick, a nylon overcoatwound on the metal core, and a #35 AWG size wire coated with a heavypolyurethane wound 1,800 turns as a secondary winding.

Such a sensing transformer with a core of magnetically permeablematerial, such as iron, generates a voltage signal reasonably accuratelyrepresentative of the current in the power cable over a certain normalload range. However, iron and other magnetically permeable materialshave hysteresis and other nonlinear responses to changing magneticfields that result in a nonlinear relationship between current in thepower cable and the voltage signal produced in a transformer coil havingsuch a core. The nonlinearity of such responses is especiallysignificant with large variations in load current and frequency. Toprovide a more linear measurement of power, “air core” transformers havebeen designed using wire wrapped on a core made of material having a lowmagnetic permeability, such as one of plastic or nylon. Without amagnetically permeable core, however, the transformer winding generatesrelatively small voltage levels in response to power cable currents. Anexemplary air core transformer has the following construction: core ofnylon, outside diameter of 1.375 inches, inside diameter of 1.125inches, strip width of 0.500 inches, and a #35 AWG size wire coated witha heavy polyurethane, wound 4,000 turns as a secondary winding. Examplesof circuitry suitable for use with an “air core” transformer aredisclosed in U.S. patent application Ser. No. 08/300,732, assigned tothe same assignee, and incorporated herein by reference.

The ends of the secondary winding 40 a and 40 b of the transformer 34are electrically connected to an input circuit 50. The input circuit 50is designed to convert the voltage signal received from the transformer34 to either a signal representative of the changing current in thepower cable or a circuit condition at the output terminal 41 a and 41 brepresentative of the changing current in the power cable. The signal orcircuit condition is provided to transmission lines 54 and 56 which areconnected to the control panel 20. For example, the signal could be acurrent signal, voltage signal, or some sort of frequency modulation,amplitude modulation, or digital encoding. The circuit condition, forexample, could be a short circuit, open circuit, or other suitable typeof condition. The input circuit 50 can be designed and constructed inany manner, so long as it converts the voltage signal output from thetransformer 34 to an appropriate corresponding signal or circuitcondition. Several exemplary input circuit designs are described below.A light emitting diode 58 is electrically connected to the input circuit50 and is illuminated when current is sensed within the power cable. Apotentiometer 59 allows adjustment of a threshold level within the inputcircuit 50 of the sensed voltage from the transformer 34.

The use of the control panel 20 or system controller provides automatedcontrol over the electrical system 10. The control panel 20 receives thesignal from the input circuit 50 or determines the circuit condition ofthe input circuit 50 via a pair of transmission lines 54 and 56. Thecontrol panel 20 in response to receiving the signal or determining thecircuit condition of the input circuit 50 analyzes the signal or circuitcondition to determine information such as power consumption,overcurrent, overvoltage, undercurrent, undervoltage, frequency, spikes,harmonics, etc. From this information the control panel 20, among otherthings, may determine that the electrical device 24 should be disabledor enabled. For example, if the current sensor indicates that a motor(not shown) for a pump is malfunctioning, then the control panel 20 mayhave that motor deactivated. If deactivation of that motor would alsoimpact another device, such as an auger within a storage tank supplyingfluids to the pump, then the control panel 20 may also deactivate themotor for the auger.

The control panel 20 is electrically connected to a switch circuit 60 bya pair of transmission lines 61 and 63. The switch circuit 60 is locatedproximate to the transformer 34 and input circuit 50. The switch circuit60, transformer 34, and input circuit 50 are all enclosed within thesingle package 30. The package is preferably mounted within the starterhousing 26.

The switch circuit 60 includes any suitable switching device, forexample, a triac or a relay, as will be described below. The triac orrelay is powered by a 24 volt AC or DC signal through the transmissionlines 61 and 63. The power on the transmission lines 61 and 63 closesthe circuit through the switch circuit 60 and maintains a short circuitbetween the output terminals 67 a and 67 b of the switch circuit 60.When power ceases to be supplied to the switch circuit 60, the outputterminals 67 a and 67 b of the switch circuit 60 are electricallyisolated from each other (open circuit). With the output terminals ofthe switch circuit 60 in an open circuit condition when the transmissionlines 61 and 63 are not powered, a safety feature for the starter 22 isprovided in the event of power failure to the control panel as will bedescribed below. Alternatively, the switch circuit 60 could be designedto be controlled by any type of suitable signal or circuit condition.

A pair of wires 70 and 72 are connected between the output terminals 67a and 67 b, respectively, of the switch circuit 60 and starter terminals74 and 76. The starter terminals 74 and 76 permit exterior control overthe operation of the starter 22. For most starters 22, when theterminals 74 and 76 are short circuited (electrically connectedtogether) the starter 22 energizes and operates the associatedelectrical device 24. Alternatively, when the terminals 74 and 76 areopen circuited (isolated from each other), the starter 22 de-energizes,or otherwise ceases the operation of the associated electrical device24. Accordingly, the open or short circuited circuit conditions appliedbetween the output terminals 67 a and 67 b of the switch circuit 60connected to the wires 70 and 72 are suitable to control the starter 22.The switch circuit 60 may alternatively be constructed to providewhatever signal or circuit condition is necessary to control theparticular starter 22, which may include a voltage signal, a currentsignal, digital signal, etc. A light emitting diode 64 is electricallyconnected to the switch circuit 60 and is illuminated when thetransmission lines 61 and 63 are powered.

Referring to FIG. 3, an electrical schematic diagram of a current sensor300 suitable to provide a full scale 0 volt to 5 volt output signal isshown. The transformer 34 encircles a power cable 23 c, producing avoltage between the ends 40 a and 40 b of its secondary winding. Theends 40 a and 40 b of the transformer secondary winding are connected tothe input circuit 50 which includes a full wave rectifier 312, connectedto a variable resistance 314 and associated capacitors 316 and 318, toscale the output of the full wave rectifier 312 to the desired range.The preferred range to interface with conventional control panels 20 is0 volts when no current within the power cable 23 c is sensed to 5 voltswhen the maximum desired level within the power cable is sensed.

Referring to FIG. 4, current sensor 320 provides either an open circuitor short circuit at its output terminals 41 a and 41 b depending onwhether the voltage signal produced in response to the current sensed bythe transformer 34 surpasses a predetermined threshold level. A variableresistor 326 sets the threshold level.

Referring to FIG. 5, current sensor 340 provides a 4-20 ma variableoutput signal at its output terminals 41 a and 41 b. When the currentsensed in the power cable 23 c is 0 then the sensor circuit 340 puts outa 4 ma signal. When the current sensed in the power cable 23 c is equalto a desired maximum, when the variable resistor 341 is correctly set,then the sensor circuit 340 puts out a 20 ma signal.

Referring to FIG. 6, an electrical schematic of a switch circuit 60 isshown. A voltage or current signal from the control panel 20 is providedto the input terminals 66 and 68 of the switch circuit 60. When anon-zero signal is received by the switch circuit 60 alight-emitting-diode 64 is illuminated to indicate that the switchcircuit 60 is energized. A diode 368, a resistor 370 and a capacitor 372rectify the signal received at input terminals 66 and 68 if it is analternating signal. The voltage imposed across the capacitor 372 is theinput to the direct current relay 374. If the signal received at inputterminals 66 and 68 is a direct voltage or current signal, then thesignal will also pass through to the relay 374. Accordingly, the switchcircuit 360 is suitable to receive both an alternating signal or directsignal. The relay 374 is energized by a high voltage signal at the inputterminals 66 and 68 and thereby its output contacts 67 a and 67 b areshorted. When the high voltage signal provided to the relay 374 is belowa threshold level, the output contacts 67 a and 67 b to the relay 374open, open-circuiting the output contacts 67 a and 67 b. The outputcontacts 67 a and 67 b are connected to the terminals 74 and 76 of aremotely located starter 22 (not shown) via wires 70 and 72 (FIG. 1). Inother words, the starter 22 is spaced apart from the switch circuit 60.

Referring to FIG. 7, an alternative switch circuit 60 a includes a pairof input terminals 66 and 68, a resistor 406, a diode 407, and acapacitor 408 to permit the use of either an alternating signal or adirect signal as the input to the input terminals 66 and 68. Anopto-isolator 410 isolates the high voltage to the input terminals 66and 68 from the output terminals 67 a and 67 b for safety. A triac 412,which is a switching device, is energized with a low voltage on the gate413 of the triac 412 to close the triac 412 creating a short circuitbetween the output terminals 67 a and 67 b. A “snubber circuit” includesa resistor 418 and capacitor 420 connected in parallel across the outputterminals 67 a and 67 b. In general, the ‘snubber circuit’ preventsfalse triggering of the triac 412 that may occur when driving aninductive load. Output terminals 67 a and 67 b are thus short circuitedor open circuited (by the operation of the triac 412) with the resultthat the terminals 67 a and 67 b exhibit a circuit condition to thestarter 22 indicative of whether the electrical device 24 controlled bythe starter 22 should be operating.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

1. A protection device for monitoring current in a power cable to anelectrical device and for controlling said electrical device in responseto a system remotely located from said protection device, the protectiondevice comprising: (a) a transformer magnetically linked with said powercable suitable for connection to said electrical device, saidtransformer producing an electrical signal at a pair of terminalsthereof in response to the presence of a changing current within saidpower cable; (b) an input circuit electrically connected to said pair ofterminals of said transformer and having an output terminal and beingelectrically connected to said transformer so as to be suitable forsensing said electrical signal, said input circuit producing, inresponse to sensing said electrical signal, one of a first signalrepresentative of said changing current in said power cable at saidoutput terminal of said input circuit, and a first circuit condition atsaid output terminal of said input circuit representative of saidchanging current in said power cable; (c) a switch circuit suitable forsensing one of a second signal and a second circuit condition of saidremotely located system and providing one of a third signal and a thirdcircuit condition, in response to sensing one of said second signal andsaid second circuit condition, said third signal and said third circuitcondition suitable for being effective to control said electrical devicewhen said electrical device is electrically connected thereto; and (d)said input circuit, said pair of terminals of said transformer, and saidswitch circuit being located within a single unitary package; whereinsaid input circuit is free from determining a value of power based uponsaid electrical signal.
 2. The protection device of claim 1 wherein saidtransformer includes a wire-wrapped toroidal core at least partiallyencircling said power cable.
 3. The protection device of claim 1 wheresaid toroidal core has a low magnetic permeability.
 4. The protectiondevice of claim 1 wherein said first signal is a current signal.
 5. Theprotection device of claim 4 wherein said current signal has a range ofmagnitude from about 4 ma to about 20 ma.
 6. The protection device ofclaim 1 wherein said first signal is a voltage signal.
 7. The protectiondevice of claim 6 wherein said electrical signal has a range ofmagnitude from about 0 volts to about 5 volts.
 8. The protection deviceof claim 1 wherein said first circuit condition is one of a shortcircuit and an open circuit.
 9. The protection device of claim 1 whereinsaid system controller is a programmable logic device.
 10. Theprotection device of claim 1 wherein said second signal is a directcurrent signal.
 11. The protection device of claim 1 wherein said secondsignal is a alternating current signal.
 12. The protection device ofclaim 1 wherein said second signal is a direct voltage signal.
 13. Theprotection device of claim 1 wherein said second signal is analternating voltage signal.
 14. The protection device of claim 1 whereinsaid switch circuit includes a relay electrically connected to saidsystem controller to sense said one of a second signal and secondcircuit condition.
 15. The protection device of claim 1 wherein saidswitch circuit includes a triac electrically connected to said systemcontroller to sense said one of a second signal and second circuitcondition, and said transformer is located within said housing.
 16. Theprotection device of claim 1 wherein said switch circuit includes anopto-isolator device.
 17. The protection device of claim 1 wherein saidswitch circuit includes a rectifier circuit to rectify said secondsignal.
 18. The protection device of claim 1 wherein said third circuitcondition is a short circuit.
 19. The protection device of claim 1wherein said third circuit.